At Wednesday’s preem of Warner Bros.’ “Project X,” co-writer Michael Bacall admitted he wasn’t much of a party animal growing up in the San Fernando Valley.

“I was a nerd in high school so I never did anything like what’s in the movie,” he recalled following the screening at the Chinese. “The producers told me and Matt Drake to go crazy. So I wrote mostly at nights with lots of coffee on breaks between working on ‘Scott Pilgrim‘ and ‘21 Jump Street.’ ”

Bacall, who began acting when he was 4, said last summer’s shoot at the Warner Ranch provided a coming-home feel. “I had a part in ‘Free Willy’ when it was shot there in 1993, so it was really comfortable to be back,” he said.

The after-party at the Lot featured perfs by Kid Cudi, Tyler the Creator and the Hundred in the Hands. Guests were also greeted by an LAPD cruiser, a bouncer with the admonition “keep your clothes on” and an array of beer pong tables — leading to dozens of hotly contested matches.

Director Nima Nourizadeh, who’s making his feature debut, admitted to some experience with the party scene growing up in London.

“I knew how to have a good time, but nothing as chaotic as this film,” he said. “This has been my life for the past two years.”